Electrical Contact Reliability Design of Automotive Connectors
Automotive Connectors place a heavy emphasis on reliable electrical contact design parameters, including contact resistance, plug-in force, and positive contact pressure.
Design of Contact Resistance for Automotive Connectors
According to the theory of electrical contact, the contact resistance R = RC + Rf + Rp, where:
Rp – Conductor resistance, which is the sum of the ohmic resistances of the terminal and lead-out wires. The size depends on the material, cross-sectional shape, and length of the terminal and lead-out wires.
RC – Concentrated resistance, the resistance that occurs when two terminals come into contact. It is impossible for their surfaces to be fully in contact, as there is point-to-point contact at the microscopic level. When current flows from one contact piece to another, there is resistance due to the contraction of the current lines, resulting in shrinkage resistance.
Rf – Film layer resistance, which is produced by adhesive films, dimming films, and thin films on the contact piece's surface.
Factors influencing contact resistance: inherent material characteristics, contact pressure, production process capabilities, etc.
Selection of Terminal Materials for Automotive Connectors
Selection of terminal material with high conductivity or low resistance (Brass has a conductivity of about 13%, phosphor bronze is about 26%, and beryllium copper can reach 40%), is the most effective way to reduce contact resistance.
The basic requirements for terminal material selection include:
Conductivity - high conductivity and low resistance to reduce contact resistance;
Ductility - helpful for terminal shaping;
Hardness - improve mechanical properties and wear resistance, increase the contact area, and reduce contact resistance;
Yield strength - in mechanical and material science definitions, it means the stress value in which the material begins to produce plastic deformation (permanent deformation). There is a large displacement within the elastic range;
Elastic modulus - a higher elastic modulus makes it easy to break the surface film, which helps to reduce the contact resistance of the film. A lower elastic modulus can increase the contact area of elastic deformation;
Stress relaxation - The terminal can still maintain its load-bearing capacity for a long time under stress or high temperature;
Hardness - reduce the wear and tear of the terminal metal.
Contact Insertion Force Design of Automotive Connectors
Among the factors affecting contact resistance, the impact of contact pressure is the greatest, but the contact pressure is generally impossible to measure.
The force required to overcome the resistance produced by elastic contacts when the contact pieces are inserted and extracted is called the contact insertion force and withdrawal force. According to Hooke's law, the greater the contact pressure, the greater the insertion and withdrawal force. Therefore, to some extent, the insertion and withdrawal force is the friction force generated between the contact pieces under the action of positive pressure of the elastic contacts.
When the insertion and withdrawal force varies within a certain range, the change in the contact resistance is more obvious. In other areas, the change of the contact resistance is relatively inert, even if the insertion and withdrawal force increases a lot, the contact resistance does not decrease significantly. From an economic perspective, it is not practically meaningful to require further reduction of contact resistance by increasing insertion and withdrawal force beyond a certain limit. Therefore, reducing contact resistance should not only be considered from the perspective of insertion and withdrawal force.
With decades of experience in the connector manufacturing industry, GREENCONN has mastered the core technology in the field of connectors and obtained the IATF 16949 certification in the automotive industry. Greenconn can provide one-stop service from new product research and development, and testing to production, ensuring that all the automotive connectors produced have the same reliable mechanical and electrical performance, empowering the interconnection solutions for the automotive industry.
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